Recently, the use of communication devices such as mobile communication devices has increased. Typically, such communication devices are used close to the body. As the use of communication devices explosively increases, much attention has been paid to an effect of electromagnetic fields generated from the communication devices on the body.
According to current researches, a connection of the effect of electromagnetic fields on the body at frequency bands used by the communication devices has not been clearly revealed. However, it is likely that the electromagnetic fields have an effect on various diseases such as leukemia and brain tumor. Therefore, electromagnetic field reduction technologies for preparation for exposure to electromagnetic fields which may be harmful will become necessary technology in the future.
Existing technologies for the electromagnetic field reduction generally employ an electromagnetic field absorber or apply the modification of a radiator structure such as antenna mismatch. Furthermore, a technology using an artificial magnetic conductor (AMC) and an electromagnetic bandgap (EBG) is applied as one of electromagnetic field radiation control technologies. In this technology, periodic metal patterns are artificially implemented in a substrate formed of dielectric or the like, in order to change the electromagnetic characteristics of a radiator.
The AMC technology may reduce the size of an antenna, and increase the gain of the antenna, thereby improving the radiation characteristics of the radiator.
Such a technology may be used to control a radiation pattern of electromagnetic fields radiated from the radiator and reduce the radiation of the electromagnetic fields toward the body, thereby protecting the body.
Since the above-described AMC technology uses a passive element, the direction of electromagnetic fields may be adjusted only in one direction at a designed frequency with limitation. Therefore, when the surrounding environment is changed, the AMC technology may not actively deal with the change.